Electric furnace.



M. M. KOHN.

ELECTRIC FURNACE.

APPLICATION FILED MAY5,I914.

Patented June 20, 1916.

INVENTOR 3 SHEETS-SHEET l- TIIF. cnnmuxm PLANocRAvH co., \YASHINGTON. D. c

M. M. KOHN.

ELECTRIC FURNACE- APPLICATION FILED MAY 5. m4.

Patented June 20, 1916.

3 SHEETS-SHEET 2.

WITNESSES lNl/EN TOR ma coLI-IMIIA PLANOGIAPH :0, WASHINGTON, D. c

M. M. KOHN. ELECTRIC FURNACE.

APPLICATION FILED MAY 5. 914.

1,187,630. Patented June 20, 1916.

3 SHEHS-SHEET 3.

ml COLUMBIA PLAIOGRAPH cm. WAIHING'ION, D. I

MILTON M. KOHN, OF NEW YORK, N. Y.

ELECTRIC FURNACE.

Specification of Letters Patent.

Patented June 20, 1916.

App1ication filed May 5, 1914. Serial No. 836,419.

T 0 all 2072,0112, it may 007106772.

Be it known that I, MILTON M. KoHN, a citizen of the United States, residing at the borough of Manhattan, in the city, county, and State of New York, have invented an Improvement in Electric Furnaces, of which the following is a specification.

My present invention relates to an elec trio furnace, and is an improvement upon the construction of an electrical heating apparatus shown and described in Letters Patent No. 1,057,745, granted to me in April 1, 1913.

The objects of my present invention are to so improve the construction of the electric furnaces made in accordance with the disclosure of the patent aforesaid, as to result in economy of construction, hence reducing the cost of the apparatus to the consumer, and also in the efficiency of the improved apparatus over that shown in the patent, so that there is a consequent increase in efiiciency and a decrease in the cost of the furnaces.

In the present case, as in the furnaces heretofore constructed by me, the apparatus comprises a housing, preferably a plurality of heating units, each tted with a heating medium and removable from the apparatus with one head thereof, together with means for not only varying the temperature produced in the heater, but also maintaining the same constant at a required degree.

In the apparatus as heretofore constructed, and as shown and described in the Letters Patent aforesaid, the housing was made of clay sections, which parts were connected by a suitable binder, the space between the housing and easing being fitted with a separate heat insulator. In my improved electric furnace, the housing is preferably made of a cellular or diatomaceous material or infusorial earth, made in blocks or slabs of suitable configurations for buildingup the housing of the furnace, which also acts as the heat insulator.

In the furnaces heretofore constructed, the heating units were non-reversible, and furthermore it was necessary to remove a head of the furnace in order to take out any of the heating units. In the present case, the heating units are preferably made reversible, or double sided, and are ar ranged, as heretofore, to be secured together in alinenient to produce the desired heating surface, and the electrical and mechanical connections are such that the units may be removed with one of the heads of the fur nace, or separately and independently of each other as heretofore.

In the furnaces heretofore constructed, the heating units were supported directly in the housing, whereas in the present instance, I prefer to employ independent supports for the heating units, which sup ports are suitably secured in the housing, in the necessary positions, and are adapted to receive the heating units and maintain the same in position.

In the furnaces, as heretofore constructed, and as shown and described in the patent aforesaid, the heads of the apparatus are made of refractory material, and broadly perform the function of closing the ends of the apparatus, whereas in the furnace constructed in accordance with my present invention, I prefer to so construct these heads that they are not likely to crack, due to the strains put thereon by reason of the great differences in temperature to which they are subjected, and also in order that they may act as a support or a partial support for the heating units, to which they are usually connected, as hereinbefore stated, that the parts may be removed together, the inner portions of the heads being preferably constructed of pure asbestos, while the outer portions are constructed of a composition of asbestos and cement or similar material.

It will furthermore be understood, in the furnaces as heretofore constructed and as shown and described in Letters Patent aforesaid, that the temperature control was effected by a rheostat suitably connected exteriorly of the heating mediums in the appa'atus, whereas in my improved construction, I prefer to employ suitable rheostator resistance coils so connected to or built in the heads or the body or housing of the apparatus as to utilize the heat generated therein, in the furnace itself, and furthermore the rheostat or resistance employed is such that the temperature control may be effected in a like manner, whether the apparatus is used on 110 or 220 volt circuits.

In the drawing, Figure 1 is a side elevation and partial central cross section on line 1, 1, Fig. illustrating an electric furnace made in accordance with my present invention. Fig. 2 is an elevation and partial cross section on line 2, 2, Fig. 1. Fig". 3 is a view similar to Fig. 1, illustrating a modified form. of the invention. Fig. l a view similar to Fig. showing the modification illustrated in Fig. Fig. 5 is a diagraminatic plan illustrating the electrical connections, the rheostat or resistance coils for controlling the current and consequently the temperature in the furnace. Fig. (3 is a POlSlXCt-ll'ti view illustrating one of the blocks forming the heating units. Fig. 7 is a similar view illustrating another form of these blocks. Fig. 8 is cross section through the rheostat terminal employed in the form of invention as applied to a different type of furnace. Fig. 9 is a transverse section showing a modified form of my invention, and Fig. 10 is a view siinila to Fig. 9, showing a stil further 1110(l1fi(2t tion of the invention.

Referring to the drawing, and particularly to Finis. 1 and 2, it will be seen that in carrying out my present invention, 1. prefer to employ a shell or casing, indicated at 10. This may be made of sheet metal or any other suitable material, and of any required dimensions and shape. At its opposite ends the shell or casing- 10 is provided with heads 11 and 12. lhe head 11 has an opening, in which a heater door 13 or removable plug is suitably titted. As illustrated, this door hinged at H and pro vided "ith a rod 15 carrying a. counterweight 16. by means of which the door may be maintained in either its normally closed position or in an open position. is hereinbefore indicated, the inner portions of these heads 11 and 12 are preferably made of a suitable fibrous material, such, for example, as pure asbestos, whereas the outer portions of these heads are preferably made of a composition of a fibrous material and a suitable cement. ll ithin the shell of the casing 10, I employ a housing, which is built up ot a plurality of suitably shaped blocks 17, made of an infusorial earth or cellular or diatoinaceous material. These blocks are so made and placed within the housing that they assume a staggered relationship with one another and may be maintained in position within the housing by use of the tie rods 18 and nuts 19. or otherwise. Surrounding; the heads 11 and 12. are annular members 11 and 1'2, through which the tie rods 18 also pass, in order to secure the blocks 17 in position permanently within the shell 10. It will be understood, however, in some instances, particularly where the furnaces are of small dimensions. the housing made of infusorial earth. cellular or diatoinaceous material. may be an integral structure, and in all cases this housing is suiiiciently heat insulating to enable me to dispense with the use of the filling material, which E have heretofore employed as a cover for the housing, to make the same sulliciently heat insulating. As illustrated in this form of the invention, I. employ a plurality of angular heat unit supports. In t les. 1 and the chamber within the furnace is-shown as square in cros section. and for this reason, in this form of rurnace four of these heat unit supports are employed, one being placed in each corner of the heating chamber. Each of these heat units supports, on its outer side, adjacent the corner, is provided with diverging ribs or flanges 2l22. adapted to be received in rece, s provided therefor in the housing blocks 17, so as to maintain the heat unit supports in position within the housing with their outer faces preferably abutting against the adjacent inner faces of the blocks comprising the housing.

On its inner side, each heat unit support 20 is provided with a central longitudinal projection or rib between which and the arms of the heat unit support there are recesses 2%, adapted to receive and maintain in position the heating units as hereinafter described. l urthermore, each of these heat unit supports is preferably provided with a bore runninglmie'itudinally thereof and also with passages 26, in suit-ably spaced positions, in the central projection or rib 23, so as to provide communication between the heating chamber and the bore 95, which latter is filled with any suitable material, which, under the influence of heat, or otherwise, will liberate certain gases to prevent the oxidization of the material or substance, indicated at 27, under treatment in the furnace chamber. or to otherwise intluence or effect the action of the heat on the material being treated.

Referring particularly to Figs. 5 and '7, it will be seen that the heat units I prefer to employ in my present invention each comprises a plurality of blocks placed in alinement with one another to obtain the necessary extent of heating surface, each block constituting a body portion 28, on the opposite surfaces of which there are series of suitably spi ced parallel under-cut grooves, indicated at 29 and 30. At opposite ends, each block is provided with flanges 31, adapted to be received in the recess 24.- in the heat unit supports 20. As will be apparent from these figures, the under-cut grooves may be made to run parallel with the end flanges, or at right angles thereto, or in one direction on one side, or in the 0pposite direction on the other side, or in bot-h directions on the same side, in which instance the grooves running in one direction must necessarily be deeper than those running in the other direction, and in both constructions the end flanges are provided with bores adapted to receive rods by which the blocks, comprising any given heat unit,

are secured in alinement with one another, and also the electrical connections between the heating medium employed with the heating unit and suitable terminals are com pleted.

Associated with each heating unit, and threaded through the under-cut grooves therein, I employ a heating medium, such, for example, as coiled resistance wires, indicated at 33.

As illustrated in Figs. 1 and 2, the rods 34, by which the blocks comprising each heating unit are secured in alinement and electric circuits through the heating medium completed to suitable terminals, may be carried directly through bores provided for this purpose in the rear head 12 of the furnace, and there provided with suitable nuts for making the necessary electrical connections, as hereinafter described. In this construction, the rods 34 permanently secure the heating units to the head 12 and in such a manner that the heating units, together with the head 12, may be simultaneously removed from the furnace by taking out the head, or, as shown in Fig. 3, these conducting and connecting rods 34 may terminate at points within the head of the furnace, which, in this instance, is indicated at 64, and at their extremities these rods may be provided with screw threads or taper ends in order to receive the tapped ends of the stem 34, or taper recesses therein which extend to the outer surface of the head, and to which necessary electrical connections may be made for placing the heating mediums, associated with the heating units, in an electrical circuit, in which construction, as will be understood, in order to remove the heating units, the stems 34 must be disconnected from the contacts on the outer surface of the rear head and the front head of the furnace removed, when the heating units, with the rods 34 and stems 34, may be withdrawn independently of one another from this end of the furnace. In some cases, the ends of the coils may extend through the head to the exterior electrical connections.

As shown diagrammatically in Fig. 5, the adjacent connecting rods 34 of the heating units in the furnace are joined together by connecting bars 35, 36 and 37, so as to complete the electric circuit through the heating mediums in these heating units, and also the corresponding connecting bars of adjacent heating units are joined by the connecting bars 38 and 39 with terminals 40 and 41.

Suitably placed on the rear head of the furnace there are also terminals 42, 43 and 44. The terminal 42 is connected to the terminal 40 by a wire 45, and the terminal 43 is connected to the terminal 41 through a wire 46, in which there is a switch 47. The terminal 44 is connected througha wire 48 with the connecting bar 36, and in this wire 48 there is a switch 49. One terminal of the switch 49 is connected by a wire 50 to a rheostat contact frame 52 which may be suitably connected or secured to the wall of the furnace. The rheostat contact frame 52 may be provided with a plurality of contacts 53, to which the ends of heat coils 53 are connected, as usual. These heat coils 53 preferably extend through suitable recesses provided therefor in the blocks comprising the housing, and consequently the heat generated in these coils, when in use, is utilized in the housing to make the same the more heat insulating and consequently to more readily maintain the desired temperature within the chamber. The other terminal 54 of the rheostat frame 52 is connected by a wire 55 with the other terminal of the switch 49.

Associated with the terminals 42, 43 and 44, I employ a socket member 56. To this lead wires 57 and 58 are connected, the lead wire 57 being divided within the socket member and leading to contacts 59 and 60, while the lead wire 58 is connected to a con tact 61. These contacts 59, 60 and 61, as will be understood, are fixed within the socket member and are adapted to receive any one of the terminals 42, 43 and 44.

One terminal of the switch 47 is connected by a wire 62 to the terminal 54 of the rheostat frame 52, while the other terminal of the switch 47 is connected by a wire 63 to a terminal 51 of the rheostat 52.

From the foregoing, it will be understood that by properly placing the socket member and the contact arm of the rheostat frame, as well as the switches 47 and 49, the current may be caused to flow through the heating mediums, either in series of multiple, and to be regulated to obtain the desired temperature, for example, with the switch 47 in the dotted line position, shown in Fig. 5, with the switch open when the socket member 56 is so placed that the terminal 42 bears against the contact 60 and the terminal 43 against the contact 61, the current will flow through the wire 45 to and through the various heating mediums, in series, to the switch 47, through the same, the wire 62, the rheostat frame 52 and coils 53, the wire 63, and thence through the wire 46 to the terminal 43 and contact 61, whereas if the socket member is so placed that the terminals 42 and 43 bear against the res'pective-contacts 59 and 60, and the terminals 44 against the contact 61, while the switches 47 and 49 are swung to the full line positions, Fig. 5, the current will flow in multiple through the heating mediums in the oppositely placed heating units to the connecting bar 36, hence to the switch 49 on the wire 55 to the rheostat frame 52, and coils and thence by the wires 48 and 50 to the terminal 44 and its contact 61.

Jer of the in order to properly cen- 1e current and consequently the tem- Also in Fig. itienal resistance quirecl nun1l resistance coils l the furnac may employ an add cut in 01' cut out any re Ciel "t pernture witlnn 1,1ezee0 11. when istnt frame nnts may be :1 111g the as shown understood ti 0 use the 1'l1e( ner by pl ne posltwn.

l, 3 the heati zed. 111 the s 5 swlteh l! 111 me 111 iull 11 it is not necessn:

the

It will further be and coils ut1l1 (:1- ss section. each of the heating units be- 1 n shifted to either 65 movable, the rod 71 bei ing provided with series of under-cut grooves 83 adapted to receive a suitably coiled wire or other heating medium.

By reference to Fig. 10, it will be seen that the lining of the heating chamber may be made of an integral heating unit 84:, which is preferably circular in cross section and provided on its exterior, at diametri cally opposite points, with ribs 85 and 86, both having bores running longitudinally through the same to receive the rods 87 like the rods 7 8, as hereinbeforedescribed. These ribs 85 and 86 are adapted to be received in grooves provided for this purpose in heating unit supports 88 and 89, each provided with diverging ribs 90-91, by which. they are secured in position in recesses provided to receive these ribs in predetermined blocks forming the housing. In this instance, as in the structure shown in Fig. 9, the heating unit, on its inner surface, is provided with series of spaced under-cut grooves 92 to receive suitably coiled wires or other equally good heating mediums.

As shown in Figs. 1 to 4, inclusive, the furnace therein illustrated may be supported upon suitable legs 93, tied by cross bars 94:, and in the forms of the invention shown in Figs. 9 and 10, the shell or casing 72 may be provided with brackets 95 which are connected to suitable standards or supports 96, by means of the bolts and set screws 97 It will furthermore be understood that while I have herein shown and described my invention as particularly applicable to an electric furnace, it may be utilized wherever possible in all forms of electrical heating apparatus. and also that the heating units may be so shaped that their faces will cause the cross section of the heating chamber to be of any desired configuration, irrespective of the shape of the furnace, and may be made integral or divided occasion may require.

By particular reference to Fig. 6, it will be understood that when this form of unit block is employed, the undercut recesses 29 or 30, depending upon which face of the block is placed toward the heating chamber of the furnace. may be employed as ventilating spaces by omitting the resistance wires in these undercut recesses which come on the inner side of the unit when placed in position, thus providing for the circulation of air between the units and the adjacent portions of the housing.

I claim as my invention:

1. An electric furnace comprising a casing, a combined housing and heat insulator of diatomaceous material therein, a plurality of heating units of refractory material, a corresponding number of heating unit supports, each provided with ribs adapted to be received in recesses provided therefor in the housing in order to maintain the said supports in position, the said supports being provided with recesses to receive and maintain in position the said heating units so that each of the same may be removed independently of the others, and a heating medium associated with each of the said heating units.

2. An electric furnace comprising a casing, a plurality of blocks of diatomaceous material arranged in a staggered relationship, a plurality of heating unit supports, each provided with longitudinal. recesses in its inner surface, ribs on the outer surfaces of the said heating unit supports, adapted to be received in recesses provided for this purpose in the said housing so as to maintain the said heating unit supports in position, a plurality of heating units adapted to be received and maintained in position in the recesses in the said heating unit supports, and a heating medium associated with each of the said heating units.

3. An electric furnace comprising a casing, a combined housing and heat insulator of diatomaceous material therein, a plurality of reversible heating units made of refractory material, a corresponding number of heating unit supports removably secured in the said housing and adapted to receive and maintain in position the said heating units so that any one of the same may be removed independently of the others, and a heating medium associated with each of the said heating units.

4i. An electric furnace comprising a casing, a housing therein consisting of a plurality of blocks of diatomaceous material placed in a staggered relationship, a plurality of heating units of refractory material each consisting of a reversible block, means for securing the members of each heating unit together, a corresponding number of heat ing unit supports, each being provided with recesses in its inner surface to receive corresponding portions of the said heating units in order that the same may be maintained in a position so that each may be removed independently of the others, ribs on the outer surface of the said heating unit supports, adapted to be received in recesses provided therefor in the said housing, so as to maintain the heating unit supports in position and to make the same removable from the housing, and a heating medium associated with each of the said heating unit supports.

5. An electric furnace comprising a casing, a heat insulating housing of cellular material therein, heating units of refractory material, supports therefor forming the walls of the chamber within the furnace, a heating medium associated with each heating unit, and means for supplying a gas from the walls thereof to the interior of the chamber of the furnace to effect the influonce of the heat on the material under treatment therein.

6. An electric furnace comprising a cas ing, a heat insulating housing of cellular material within the casing. a plurality of heati units each made of refractory ma terial. h cc spending numb-er of heat unit support wed in the said housing and each pro. ,ed with a bore running therethrough, a material placed i hin the bores of the heat unit supports for emitting a v under the influence of the heat of the furnace to eff it the action of the heat on the material being treated in the furnace, and a heating medium associated with each of the heating units.

7. in electric furnace comprising a casing, housing of diatomaceous material, composed of a plurality of blocks suitably placed within the casing. a plurality of heating units, each consisting of a series of blocks made of refractory material and placed in alinemcnt, a plurality of heating unit supports secured in the housing and adapted to receive the said heating units so that the same may be removed independently of one another and each having a hore there through, a material filling the said bore and each heating unit support, adapted under the influence of the heat of the furnace to emit a for affecting the action of the heat on the mate ial treated within the furnace, and a heating medium associated with each of the heating units.

9. in electric furnace comprising a casing, a heat-insulating housing of cellular material therein, heating unit support. projections e tending from the outer surface of the heating unit support aoapted to be received in recesses provided therefor in the said housing to maintain the said heating unit support in position, a heating medium associated with each heating unit, and a plurality of resistance coils located within the confines of the furnace with suitable electrical connections to and from the -sai d heating medium to control the passage of an electric current therethrough and consequently the resultant temperature in the chamher of the furnace.

9. An electric furnace comprising a casing, a heat insulating housing of cellular material therein, a plurality of heating units of refractory material, a corresponding number of heating unit supports, projections extending from the outer surface of each heating unit support adapted to b received in recesses provided therefor in the said housing to maintain the heating unit support in position, a heating medium associated with each of the said heating units, and a plurality of resistance coils located within the confines of the furnace with suitable electrical connections to and from the said heating medium to control the passage of an electric current therethrough and consequently the resultant temperature in the chamber of the furnace.

10. An electric furnace comprising a casin a housing within the casing built up of blocks of diatomaceous material placed therein in a stag ered relationship, a nlurality of heating units of refractm'y material, each comprising pl irality of blocks placed in alinement, a plurality of heating unit supports secured in the said housing and adapted to eceire and maintain the said heating units in position therein and each provided with a bore running longi tudinally therethrough, a material within the bore in each of the said heating unit supgorts for emitting a gas under the influence of the temperature of the furnace to affect the action of the heat on the material under treatment in the furnace, a heating medium associated with each of the said heating units, and a plurality of resistance coils within the confines of the furnace, together with electrical connections between the same and the said heating mediums for controlling the passage of an electric current therethrough and the consequent resultant temperature in the chamber of the furnace.

11. An electric furnace comprising a casing, a heat insulating housing of cellular material therein, insulating heads fixed at opposite ends of the said casing, a heating unit of refractory material, a heating unit support secured in the said housing and adapted to receive and maintain the heating unit in position therein, means for connecting the said heating unit to one of the said heads so that the same is removable there with, and a heating medium associated with the said heating unit.

12. An electric furnace comprising a casing, a heat insulating housing of cellular material therein, insulating heads fixed at opposite ends of the said casing, a heating unit of refractory material, a heating unit support secured in the said housing and adapted to receive and maintain the heating unit in position therein, means for connecting the said heating unit to one of the said heads so that the same is removable therewith, a heating medium associated with the said heating unit, and means for controlling the passage of an electrical current through said heating medium to vary the resultant temperature in the chamber of the furnace.

13. An electric furnace comprising a casing, a heat insulating housing of cellular material therein. a head at the end of the furnace. means for connecting a portion of the head to the said housing to maintain the same in position within the said casing, a plurality of heating units, each made of refractory material, a corresponding number of heating unit supports secured in the housing and adapted to receive and maintain the said heating units in position therein, means for connecting the said heating units to a portion of one of the said heads, With which the same are removable, a heating medium associated With each of the said heating units, and a plurality of resistance coils placed Within the confines of the furnace and electrically connected to the said heating mediums so as to control the flOW to an electric current therethrough to vary the re sultant temperature in the chamber of the furnace. I

14L. An electric furnace comprising a casing, a heat insulating housing of cellular material therein, a head at the end of the furnace, means for connecting a portion of the head to the said housing to maintain the same in position within the said casing, a nlurality heating units, each made of rerractory material, a corresponding number of heating unit supports secured in the housing and adapted to receive and maintain the said heating units in position and each. having a longitudinal bore therein, a material Within the bore of each heating unit support adapted under the influence of the heat of the furnace to emit a gas to affect the action of the heat of the furnace on the material under treatment therein, means for connecting the said heating units to a portion of one of the said heads, with which the same are removable, a heating medium associated with each. of the said heating units, and a plurality of resistance coils placed Within the confines of the furnace and electrically connected to the said heating mediums so as to control the flow to an electric current therethre-ugh to vary the resultant temperature in the chamber of the furnace.

15. An electric furnace comprising a casing, a heat insulating housing therein of cellular material, a heating unit of refractory material, a heating unit support secured in the said. housing and adapted to receive and maintain the said. heating unit in position so that the same may be slidably removed from the furnace, a heating medium associated with the said heating unit, and means for connecting the heating mediums in electric circuits of different voltages so as to control and maintain a uniform temperature with in. the chamber of the furnace, irrespective of the voltage of the circuit.

16. An electric furnace comprising a casing, a unitary housing and heat insulator of diatoma ceous material therein, a plurality of heating units each consisting of a number of blocks of refractory material placed in alinement, means for securing together the members of each heating unit, supports secured in the said housing and adapted to receive and maintain in position the said heating units so that each of the same may be removed independently of the others a heating medium associated With each heating unit, and means for connecting the heating mediums in electric circuits of different voltages so as to central and maintain a uniform temperature Within the chamber of the furnace, irrespective of the voltage of the circuit.

17. An electric furnace comprising a casing, a heat insulating housing of cellular material therein, a head at the end of the furnace, means for connecting a portion of the head to the said housing to maintain the same in position xvi hin the said casing,a plurality of heating units, each made of refractory material, a corresponding number of heating unit supports secured in the housing and adapted to receive and maintain the said heating units in position and each having a longitudinal bore therein, a material Within the bore of each heating unit support adapted under the influence of the heat of tne furnace to emit a gas to affect the action of the heat of the furnace on the material under treatment therein, means for connecting the said heating units to a. portion of one of the said heads, With which the same are removable, a heating medium associated with each of the heating units, a plurality of resistance coils placed Within recesses provided. therefor in the Walls of the furnace, a contact box having terminals to Which the ends of the resistance coils are connected, and means for connecting the said coils and contact box With an electric circuit so as to control the flow of the electric current therethrough to vary the resultant temperature in the chamber of the furnace.

18. An electric furnace comprising a casing, a housing and heat insulator within the casing built up of blocks of cellular material placed therein in a staggered relationship, plurality of heat units, members l'iaving projections thereon. adapted to be received in recesses provided therefor in the housing and heat insulator to secure the said members in place and maintain the position of the blocks of cellular material of which the said housing and heat insulator is made, and a heating medium associated with each of the said heating units.

19. An electric furnace comprising a casing, a housing and a heat insulator Within the casing, a plurality of heating units, support members secured in the said housing and heat insulator for receiving and maintaining in position the said heating units. a heating medium associated with each of the said heating units. seri s of resistances Within the confines of the furnace and devices associated with the Walls of the furnace eX- tcriorly thereof for controlling the passage of an electric current through the said series of resistances.

20. An electric furnace comprising a casing, a combillfitl housing and heat insulator of cellular material therein a heating unit support secured in said housing and insulator, a heating medium, and a heating unit adapted to be received in said support and to contain the said heating medium, and made of refractory material to absorb and retain heat. the surface of the heating unit being relatively large compared to that of the heating medium.

21. An electric furnace comprising a casing, a combined housing and heat insulator of cellular material therein, a heating unit support secured in said housing and insulater, a heating medium, and a heating unit adapted to be received in said support and to contain the said heating medium, and

made of refractory material to absorb and retain heat, the surface of the heating unit being relatively large compared to that of the heating medium, and resistance coils located within the confines of the furnace with suitable electrical connections to and from the said heating medium to control the passage of an electric current therethrough and consequently the resultant temperature in -35 the chamber of the furnace.

Signed by me this 30th day of April, 191i.

LHLTON M. KOHN.

\Vitnesses Bnirrim M. r-rLLnN, J. B. Ln BLANG.

Copies of this. patent may be obtained for five cents each, by manning the "Commissioner or Iatcntz. Washington, D. G. 

